The invention relates to a device for testing electric circuits provided on boards and components of electric circuits provided on boards, in which device during operation a board comprising electric components to be tested lies fixedly against a support of the device as a result of an underpressure in a first chamber, and a contact plate which is movable in a direction transverse to the board is in a position in which the board is electrically connected to a test unit of the device as a result of a pressure difference between the first chamber and a second chamber.
A device of the kind mentioned in the opening paragraph known from U.S. Pat. No. 4,115,735 is provided with a first and a second contact plate, the first contact plate being positioned between the support and the second contact plate. Both contact plates are provided with a set of test probes which extend in a direction transverse to the board to be tested. Openings are provided in the first contact plate in which the test probes of the second contact plate can be shifted. In the known device, the first chamber is situated between the board and the first contact plate, while the second chamber is situated between the two contact plates. When an underpressure is provided in the first chamber only, the test probes of the first contact plate only come into contact with the board, so that components of the circuit can be tested. When an underpressure is applied in both chambers, all test probes come into contact with the board and the operation of the entire circuit can be tested.
A disadvantage of the known device is that the test probes of the second contact plate must fit accurately in the openings of the first contact plate in order to achieve a satisfactory sealing between the two chambers. This leads to comparatively high manufacturing costs. A further disadvantage of the known device is that the contact plates are difficult to replace, so that the known device is in principle only suitable for testing one type of board. Finally, when an underpressure is applied in the first chamber or in both chambers of the known device, a number of test probes is brought into contact with the board while the underpressure simultaneously secures the board on the support. It is possible for the test probes to come into contact with the board too soon then, so that the board will not lie correctly on the support or will even be damaged.